Relation between cholesterol, membrane fluidity, and α-secretase
activity. (A) Secretion of APPsα as a function of
cellular cholesterol amount and of fluorescence anisotropy in membranes
of HEK cells. HEK cells were incubated with 10 mM MβCD for various
times (0, 2, 5, 10, 20, 30 min) to remove defined cholesterol amounts.
After 4 h, the medium was collected, and secreted APPsα was
identified as described in Fig. 1. The cell pellet was split for
determination of cellular cholesterol and protein content and for
measurements of 1,6-diphenyl-1,3,5-hexatriene steady-state fluorescence
anisotropy in cell membranes. The data are expressed as percentage of
control and are the averages ± SD of at least three experiments.
(B) Influence of steroids on secretion of APPsα from
HEK ADAM 10 cells, which were incubated in the presence of 10 mM MβCD
for 30 min at 37°C. Subsequently, cells were incubated in the
presence of 0.3 mM steroid–MβCD complexes for 30 min at
37°C.